A device of this kind is known, for example, from DT-AS No. 22 12 135, for paper pictures; corresponding constructions for photoplates are disclosed in German Patent Specifications Nos. 179 675 and 224 700.
The principle of these known devices is relatively simple. By means of a hook attached to the slider member, the uppermost picture of a pile of pictures lying in the housing is drawn away over a separator and when the slider member is pushed back in again is guided under the separator which is arranged in the housing, so that it goes under the pile. In all of the known constructions a spring arrangement is provided which presses against the pile from below so as to urge the uppermost picture (or the uppermost photoplate) against the viewing window or an illumination aperture in the housing.
This means that when reinserting the picture or plate it must be pushed between the spring arrangement and the pile disposed in the housing, with the result that the relative displacement occurring under spring pressure, on account of the high forces of friction, may result in the surface of the picture being scratched. In addition the spring arrangement must be carefully dimensioned since it must be able to extend enough to press a single picture against the viewing window (when the "pile" consists only of one picture), but must be sufficiently pliable still to permit the picture to be inserted when the pile is of maximum thickness. When the device is not in use the pictures are nevertheless constantly under the spring pressure, which when, for example, the photos are not quite dry, can lead to sticking. The removal and insertion of the pictures under spring pressure is troublesome and complicated for the user.